Grease a 9-inch loaf pan with oil or cooking spray. Reserve.
Combine dry ingredients: In a medium size bowl, combine the flour, baking powder, baking soda and salt. Reserve.
Combine wet ingredients: In a large bowl, whisk the eggs, sugar and lemon zest until pale and fluffy. Add the yogurt, oil and vanilla extract, whisking until smooth.
Make the batter: Gently add the dry ingredients to the wet ingredients, using a wooden spoon. Mix until smooth, but be careful not to over mix or the cake can develop gluten and lose the fluffy crumb.
Bake: Pour the batter into the prepared pan and bake for 50 to 60 minutes, or until a cake tester (or toothpick) inserted in the center comes out clean. Remove from oven and allow it to cool in the pan for 10 minutes. Then, carefully remove from the pan to a cooling rack, placed over a baking sheet.
Glaze: If making the glaze, cook the passion fruit puree in a small saucepan, over medium-high heat, until reduced by half. Remove from the stove and stir in the confectioners sugar and yogurt, mixing vigorously until thick and smooth. When cake is cool, pour the passion fruit glaze over it, sprinkle the poppy seeds and allow it to dry for 30 minutes before serving.
Can be made 3 days ahead. Store airtight at room temperature.